Dynamic spinal stabilization with rod-cord longitudinal connecting members

ABSTRACT

A dynamic fixation medical implant having at least two bone anchors includes a longitudinal connecting member assembly having at least one transition portion and cooperating outer sleeve, both the transition portion and sleeve being disposed between the two bone anchors. In a first embodiment, the transition portion includes a rigid length or rod having apertures therein for tying or otherwise attaching the rigid length to a second rigid length or to a flexible cord. Slender ties or cords extend through a plurality of apertures in the rigid lengths or are threaded, tied or plaited to the larger flexible cord or cable. In a second embodiment, a transition portion includes slender ties of a cord that are imbedded in a molded plastic of a more rigid member. The outer sleeve may include compression grooves. The sleeve surrounds the transition portion and extends between the pair of bone anchors, the sleeve being compressible in a longitudinal direction between the bone anchors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/896,439, filed May 17, 2013, now U.S. Pat. No. 10,470,801, which is acontinuation of U.S. application Ser. No. 12/006,460, filed Jan. 3,2008, now U.S. Pat. No. 8,475,498, which claimed the benefit of U.S.Provisional Application No. 60/922,465, filed Apr. 9, 2007; U.S.Provisional Application No. 60/898,870, filed Feb. 1, 2007; and U.S.Provisional Application No. 60/880,969, filed Jan. 18, 2007, all ofwhich are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members for such assemblies, the connectingmembers being attached to at least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist flexure, extension, torsion, distraction and compression,and thus substantially immobilize the portion of the spine that is to befused. Thus, longitudinal connecting members are typically uniform alongan entire length thereof, and usually made from a single or integralpiece of material having a uniform diameter or width of a size toprovide substantially rigid support in all planes.

Fusion, however, has some undesirable side effects. One apparent sideeffect is the immobilization of a portion of the spine. Furthermore,although fusion may result in a strengthened portion of the spine, italso has been linked to more rapid degeneration due to increasedstresses and even hyper-mobility and collapse of spinal motion segmentsthat are adjacent to the portion of the spine being fused, reducing oreliminating the ability of such spinal joints to move in a more normalrelation to one another. In certain instances, fusion has also failed toprovide pain relief.

An alternative to fusion and the use of more rigid longitudinalconnecting members or other rigid structure has been a “soft” or“dynamic” stabilization approach in which a flexible loop-, S-, C- orU-shaped member or a coil-like and/or a spring-like member is utilizedas an elastic longitudinal connecting member fixed between a pair ofpedicle screws in an attempt to create, as much as possible, a normalloading pattern between the vertebrae in flexion, extension,distraction, compression, side bending and torsion. Problems may arisewith such devices, however, including tissue scarring, lack of adequatespinal support and lack of fatigue strength or endurance limit. Fatiguestrength has been defined as the repeated loading and unloading of aspecific stress on a material structure until it fails. Fatigue strengthcan be tensile or distraction, compression, shear, torsion, bending, ora combination of these.

Another type of soft or dynamic system known in the art includes boneanchors connected by flexible cords or strands, typically made from aplastic material. Such a cord or strand may be threaded throughcannulated spacers that are disposed between and in contact withadjacent bone anchors when such a cord or strand is implanted, tensionedand attached to or compressed against the bone anchors. The spacerstypically span the distance between the bone anchors, providing limitson the bending movement of the cord or strand and thus strengthening andsupporting the overall system. Such cord or strand-type systemstypically require specialized bone anchors and tooling for tensioningand holding the chord or strand in the bone anchors. Thus a majordisadvantage of such cord and spacer systems is their lack ofinterchangeability with more rigid rod systems, especially those systemsthat incorporate polyaxial screws as bone anchors.

The complex dynamic conditions associated with spinal movement thereforeprovide quite a challenge for the design of more flexible and/or elasticelongate longitudinal connecting members that exhibit an adequatefatigue strength to provide stabilization and protected motion of thespine, without fusion, and allow for some natural movement of theportion of the spine being reinforced and supported by the elongateelastic or flexible connecting member. A further challenge aresituations in which a portion or length of the spine requires a morerigid stabilization, possibly including fusion with deformitycorrection, while another portion or length may be better supported by amore dynamic component that allows for protected movement or stressrelief, especially adjacent to a long rigid rod construct. In such casesa more rigid longitudinal connecting member can be attached to a cordmember of varying length.

SUMMARY OF THE INVENTION

Longitudinal connecting member assemblies according to the invention foruse between at least two bone anchors provide dynamic, protected motionof the spine and may be extended to provide additional dynamic sectionsor more rigid support along an adjacent length of the spine, withfusion, if desired. A longitudinal connecting member assembly accordingto the invention includes a transition or connection portion disposedbetween the bone anchors, the transition portion having at least onesubstantially rigid portion with at least one aperture and at least onetie, such as a slender cord, extending through the aperture. In certainembodiments, first and second rigid longitudinal connecting memberportions that are each attached to a bone anchor each include aplurality of apertures. Discrete ties in the form of slender cords orstrands loop through the apertures of both the first and second rigidportions, providing a flexible connection therebetween. In otherembodiments, ties that are integral with or otherwise attached to alarger longitudinal connecting member cord are threaded or laced throughapertures in a more rigid substantially solid longitudinal connectingmember, providing a flexible transition between the flexible cord thatis attached to a first bone attachment structure and a rod or othershaped longitudinal member that is attached to a second adjacent boneattachment structure. In other embodiments according to the invention,ties or strands that are integral with a flexible longitudinalconnecting member cord are attached to a solid molded plasticlongitudinal connecting member, the ties or strands being imbedded inthe connecting member, either by placement thereof within the memberduring a molding process or by drilling and plugging the member with thestrands with application of an adhesive, thus forming a transitionportion that is substantially as rigid as a remainder of the connectingmember. A plastic connecting member portion for use with the inventionmay range in rigidity from being quite rigid (no outer sleeve required)to being flexible (requiring an outer sleeve).

Transition portions according to the invention typically further includean outer sleeve or spacer that surrounds the transition between the cordand/or ties and the rigid portion or portions, the sleeve extendingbetween a pair of adjacent bone anchors and in contact therewith. Thetransition portion and the outer sleeve cooperate dynamically, bothfeatures having some flexibility, with the outer sleeve primarilyprotecting and limiting flexing movement of the inner transitionportion. The outer sleeve may include a grooved portion that may becompressed upon installation between two bone anchors.

A variety of embodiments according to the invention are possible. Forexample, both a rod-to-rod transition portion and a rod-to-cordtransition portion may be included in the same longitudinal connectingmember. Rods or other substantially rigid structures having differentmeasures of rigidity may be connected according to embodiments of theinvention. Either rigid lengths or flexible cords may be of greater orlesser lengths for attaching to one or a plurality of bone anchors.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to overcome one ormore of the problems with bone attachment assemblies described above. Anobject of the invention is to provide dynamic medical implantstabilization assemblies having longitudinal connecting members thatinclude both rigid and more flexible sections or lengths, the flexiblesections allowing for at least one of bending, torsion, compression anddistraction of the assembly. Another object of the invention is toprovide such an assembly wherein the flexible section or sections areinsertable into a protective outer sleeve. A further object of theinvention is to provide such an assembly wherein the outer sleeve may becompressed upon installation. A further object of the invention is toprovide dynamic medical implant longitudinal connecting members that maybe utilized with a variety of bone screws, hooks and other bone anchors.Another object of the invention is to provide a more rigid or solidconnecting member portion or segment, if desired, such as a solid rodportion integrally linked to one or more flexible portions or segments.Additionally, it is an object of the invention to provide a lightweight,reduced volume, low profile assembly including at least two bone anchorsand a longitudinal connecting member therebetween. Furthermore, it is anobject of the invention to provide apparatus and methods that are easyto use and especially adapted for the intended use thereof and whereinthe apparatus are comparatively inexpensive to make and suitable foruse.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a dynamic fixation longitudinalconnecting member according to the invention including first and secondrigid rod portions and a flexible transition/connection portion.

FIG. 2 is a front elevational view of the connecting member of FIG. 1and further including a wound cord cover.

FIG. 3 is a front elevational view of the connecting member of FIG. 2and further including an outer sleeve.

FIG. 4 is a perspective view of the connecting member of FIG. 3 shownwith a pair of cooperating bone screws.

FIG. 5 is a front elevational view of the connecting member and bonescrews of FIG. 4.

FIG. 6 is a front elevational view of a second embodiment of a dynamicfixation longitudinal connecting member according to the invention,shown with a pair of bone screws, with portions broken away to show thedetail thereof.

FIG. 7 is a front elevational view of a third embodiment of a dynamicfixation longitudinal connecting member according to the invention,shown with three bone screws, with portions broken away to show thedetail thereof.

FIG. 8 is a front elevational view of a fourth embodiment of a dynamicfixation longitudinal connecting member according to the invention,shown with four bone screws, with portions broken away to show thedetail thereof.

FIG. 9 is a front elevational view of a fifth embodiment of a dynamicfixation longitudinal connecting member according to the invention,shown with three bone screws, with portions broken away to show thedetail thereof.

FIG. 10 is an enlarged perspective and exploded view of the connectingmember of FIG. 1, shown without the connecting ties.

FIG. 11 is an enlarged and partial perspective view of the connectingmember of FIG. 10, with portions broken away to show the detail thereof.

FIG. 12 is an enlarged and partial front elevational view of theconnecting member of FIG. 1.

FIG. 13 is an enlarged and partial front elevational view of theconnecting member of FIG. 6.

FIG. 14 is an enlarged and partial front elevational view of a cord foruse in a sixth embodiment of a dynamic fixation longitudinal connectingmember according to the invention.

FIG. 15 is an enlarged and partial front elevational view of the cord ofFIG. 14 attached to a plastic member further showing the sixthembodiment according to the invention.

FIG. 16 is an enlarged front elevational view of the sixth embodiment ofa connecting member according to the invention, showing the cord andrigid member of FIG. 15 with a sleeve.

FIG. 17 is an enlarged cross-sectional view taken along the line 17-17of FIG. 16.

FIG. 18 is an enlarged front elevational view of the connecting memberof FIG. 16 shown with a pair of bone screws.

FIG. 19 is an enlarged and exploded perspective view of a polyaxial bonescrew assembly shown with a dynamic longitudinal connecting member.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the connecting member assemblies of theapplication and cooperating bone anchors in actual use.

With reference to FIGS. 1-5 and 10-12, the reference numeral 1 generallydesignates a non-fusion dynamic stabilization longitudinal connectingmember assembly according to the present invention. The connectingmember assembly 1 generally includes first and second substantiallyrigid members 6 and 7 with a central, dynamic connection or transitionportion or segment 8 disposed therebetween. A tie or a plurality of ties10 link the rigid members 6 and 7 at the central segment 8. The ties 10may be any flexible elongate material that fastens, secures or unitesthe rigid members 6 and 7, including, but not limited to cords, threads,strings, bands, or fibers that may be single or multiple strands,including twisted, braided or plaited materials. The central segment 8can further include an inner discrete bumper 11, a wound cover 12 and anouter sleeve or spacer 14.

Each of the illustrated rigid members 6 and 7 are substantiallycylindrical with one or more circular cross-sections along a lengththereof. However, it is foreseen that the members 6 and 7 may have otherforms, including but not limited to oval, square and rectangularcross-sections as well as other curved or polygonal shapes. It isforeseen that the member 6 and 7 may be of different materials,different shapes or different sizes, and thus one member may be morerigid or more flexible than the other member. The members 6 and 7 eachare of a length for cooperating with at least one and up to a pluralityof bone attachment members, such as bone screws or hooks. In theillustrated embodiment the rigid members 6 and 7 include respective endportions 16 and 17 of a larger diameter being integral or fixed withrespective portions 20 and 21 of smaller diameter. A tapered portion 24is disposed between the portion 16 and the portion 20. A tapered portion25 is disposed between the portion 17 and the portion 21. In someoperational embodiments, the bumper 11 may be disposed between and abutagainst the portions 20 and 21, as illustrated in FIG. 12. As will bedescribed in greater detail below, the bumper 11 and the portions 20 and21 are connected by the ties 10; the wound cord cover 12 wraps about theportions 20 and 21 and the bumper 11, forming the central connection ortransition portion 8; and the connection portion 8 is received in theouter sleeve or spacer 14. The dynamic connecting member assembly 1cooperates with at least a pair of bone anchors, such as the polyaxialbone screws, generally 30 and cooperating closure structures 32 shown inFIGS. 4 and 5, the assembly 1 being captured and fixed in place at thelarger diameter rigid end portions 16 and 17 by cooperation between thebone screws 30 and the closure structures 32. The sleeve 14 can be cutto size and is shaped to closely fit between pairs of bone screws 30 orother bone anchors or implants, cooperating with the wrapped centralconnection portion 8 to support adjacent vertebrae.

Because the end portions 16 and 17 are substantially solid andcylindrical, the connecting member assembly 1 may be used with a widevariety of bone anchors already available for cooperation with rigidrods including fixed, monoaxial bone screws, hinged bone screws,polyaxial bone screws, and bone hooks and the like, with or withoutcompression inserts, that may in turn cooperate with a variety ofclosure structures having threads, flanges, or other structure forfixing the closure structure to the bone anchor, and may include otherfeatures, for example, break-off tops and inner set screws. The boneanchors, closure structures and the connecting member assembly 1 arethen operably incorporated in an overall spinal implant system forcorrecting degenerative conditions, deformities, injuries, or defects tothe spinal column of a patient.

The illustrated polyaxial bone screw 30 includes a shank 40 forinsertion into a vertebra (not shown), the shank 40 being pivotallyattached to an open receiver or head 41. The shank 40 includes athreaded outer surface and a central cannula or through-bore 42 disposedalong an axis of rotation of the shank, the through-bore 42 extendingbetween a top surface (not shown) and a bottom surface 44 of the shank40. The bore 42 provides a passage through the shank interior for alength of wire or pin inserted into the vertebra prior to the insertionof the shank 40, the wire or pin providing a guide for insertion of theshank 40 into the vertebra.

The receiver 41 has a pair of spaced and generally parallel arms 45 thatform an open generally U-shaped channel 46 therebetween that is open atdistal ends of the arms 45. In the illustrated embodiment, each of thearms 45 includes a substantially cylindrical outer surface 47 disposedbetween a pair of substantially flat, parallel faces 48. The faces 48are sized and shaped to engage end surfaces of the sleeve or spacer 14as will be described in greater detail below. Each of the arms 45 alsoincludes a radially inward or interior surface 50 having a discontinuousguide and advancement structure mateable with cooperating structure onthe closure structure 32. In the illustrated embodiment, the guide andadvancement structure is a partial helically wound flangeform configuredto mate under rotation with a similar structure on the closure structure32. However, it is foreseen that the guide and advancement structurecould alternatively be a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe closure structure 32 downward between the receiver arms 45 andhaving such a nature as to resist splaying of the arms 45 when theclosure 32 is advanced into the U-shaped channel 46.

Each of the arms 45 also includes a V-shaped or undercut tool engagementgroove 51 formed on an outer surface thereof which may be used forholding the receiver 41 with a holding tool (not shown) havingprojections that are received within the grooves 51 during implantationof the shank 40 into the vertebra (not shown). The grooves 51 may alsocooperate with a holding tool during bone screw assembly and duringsubsequent installation of the connecting member assembly 1 and theclosure structure 32. It is foreseen that tool receiving grooves orapertures may be configured in a variety of shapes and sizes and bedisposed at other locations on the receiver arms 45.

The shank 40 and the receiver 41 may be attached in a variety of ways.For example, a spline capture connection as described in U.S. Pat. No.6,716,214 and incorporated by reference herein, may be used. Polyaxialbone screws with other types of capture connections may also be usedaccording to the invention, including but not limited to, threadedconnections, frictional connections utilizing frusto-conical orpolyhedral capture structures, integral top or downloadable shanks, andthe like. Also, as indicated above, polyaxial and other bone screws foruse with connecting members of the invention may have bone screw shanksthat attach directly to the connecting member or may include compressionmembers or inserts that cooperate with the bone screw shank, receiverand closure structure to secure the connecting member assembly to thebone screw and/or fix the bone screw shank at a desired angle withrespect to the bone screw receiver that holds the longitudinalconnecting member assembly. Furthermore, although the closure structure32 of the present invention is illustrated with the polyaxial bone screw30 having an open receiver or head 41, it foreseen that a variety ofclosure structure may be used in conjunction with any type of medicalimplant having an open or closed head, including monoaxial bone screws,hinged bone screws, hooks and the like used in spinal surgery.

To provide a biologically active interface with the bone, the threadedshank 40 may be coated, perforated, made porous or otherwise treated.The treatment may include, but is not limited to a plasma spray coatingor other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

The longitudinal connecting member assembly members 6 and 7 may be madefrom metal, metal alloys or other suitable materials, including plasticpolymers such as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcarbon fiber reinforced PEEK. According to the invention, the members 6and 7 may be made from the same material or from different materials.For example, the member 6 may be made from a very rigid titanium alloyor a commercially pure titanium, while the member 7 may be made from amore flexible plastic polymer. The bumper 11 and the outer sleeve orspacer 14 may be made of a variety of materials including metals,plastics and composites. The illustrated bumper 11 and sleeve 14 aremade from a plastic, such as a thermoplastic elastomer, for example,polycarbonate-urethane. In certain embodiments, in order to reduce theproduction of micro wear debris, the sleeve 14 inner surfaces may becoated with an ultra thin, ultra hard, ultra slick and ultra smoothcoating, such as may be obtained from ion bonding techniques and/orother gas or chemical treatments.

The ties 10 and the cord that is wound about the transition or centralconnection portion 8 to provide the cord cover 12 may be made from avariety of materials, including polyester or other plastic fibers,strands or threads, such as polyethylene-terephthalate. Such cord andcord-like materials usually are placed under axial tension along theportion 8 during installation to facilitate a stable connecting memberassembly, but typically do not illustrate elastic properties, such asany significant additional axial distraction after the assembly 1 isoperatively assembled. However, it is foreseen that in some embodiments,the ties 10 and the cord cover 12 may be made of a plastic or rubber(natural or synthetic) having elastic properties, allowing for somefurther distraction of the central connection portion 8 at the ties 10during operation thereof. The bumper 11 may be sized and chosen from arange of rigid to elastic materials so as to provide for a relativelymore rigid assembly 1 or a relatively more flexible assembly 1 withrespect to flex, bendability and/or compressibility along the centralconnection/transition portion 8.

Returning to the longitudinal connecting member rigid members 6 and 7,the cylindrical portions 20 and 21 of the respective rigid members 6 and7 each include a respective end surface 53 and 54 and a plurality ofthrough apertures or bores 56, each running perpendicular to a centrallongitudinal axis of the member 20 or 21 as illustrated in FIG. 11. Inthe embodiment shown, each portion 20 and 21 has a total of six throughbores 56 spaced along a length of the member running between therespective tapered portions 24, 25 and the respective end surfaces 53,54 and disposed in a spaced helical pattern about the cylindricalportion 20, 21. In the illustrated embodiment six ties or slender cords10 are sized and shaped for being laced through a bore 56 of each of theportions 20 and 21 and over the bumper 11 in a pattern as best shown inFIG. 12, thus making six discrete looped connections 10 a, 10 b, 10 c,10 d, 10 e and 10 f between the portion 20 and the portion 21 andcapturing the bumper 11 therebetween. See, for example, the loop 10 athat is shown on either side of the portions 20 and 21 in FIG. 12 andfurther shown in phantom extending through the bores 56, illustratingthe discrete nature of each loop. It is also foreseen that inalternative embodiments, greater or fewer than six ties or even a singletie 10 may be laced through numerous apertures in the portions 20 and 21to connect the portion 20 with the portion 21. In the illustratedembodiment, ends of each of the elongate ties 10 are knotted, fused orotherwise secured to provide each discrete loop 10 a, 10 b, 10 c, 10 d,10 e and 10 f.

As illustrated in FIG. 10, the bumper 11 is substantially cylindricaland includes outer grooves 60 sized and shaped to receive the ties 10and thereby provide a channel for each tie 10 to aid in a uniformalignment of the tie 10 between the portions 20 and 21. The bumper 11further includes substantially planar opposed front and back surfaces 62and 63 for contact with respective surfaces 53 and 54 of the portions 20and 21.

As illustrated in FIG. 2, the cord cover 12 is also a strand or cordthat is wrapped about the portions 20 and 21 and the bumper 11 and thensecured thereto by tying, fusing or otherwise fixing. The cord cover 12may be made out of a variety of materials, including polyester fiber.When the mid portion 8 formed by the portions 20 and 21, bumper 11, theties 10 and the cord cover 12 is fixed to bone screws 30 by engagementof the end portions 16 and 17 with such screws, the tie-connectedmid-portion 8 in combination with the sleeve 14 provides relief (e.g.,shock absorption) and limited movement with respect to flexion,extension, torsion, distraction and compressive forces placed on theassembly 1.

With particular reference to FIG. 3, the sleeve or spacer 14advantageously cooperates with the corded 12 central connection ortransition portion 8, providing limitation and protection of movement ofthe portion 8. The sleeve 14 also protects patient body tissue fromdamage that might otherwise occur in the vicinity of the corded centralportion 8. Thus, the sleeve 14 is sized and shaped for substantiallyeven and precise alignment and substantial contact between flat endfaces 68 and 69 of the sleeve 14 and cooperating flat side surfaces 48of the receivers 41. Furthermore, as will be discussed in greater detailbelow, in certain embodiments according to the invention, when thesleeve 14 is implanted, and the closure structures 32 are tightened, thetools utilized to implant the assembly 1 and/or the bone screws 30 maybe manipulated so as to axially compress the sleeve 14, nowsubstantially coaxial with the central connection portion 8 axis A,between facing surfaces 48 of adjacent receivers 41. In someembodiments, such compression during installation results in someadditional tension and/or distraction of the ties 10 of the centralconnection portion 8 when the implantation tools are removed from thebone screws 30, as the sleeve surfaces 68 and 69 then press against thefacing bone screw surfaces 48, but the connection portion 8 is otherwisefixed with respect to each of the bone screws 30 as the portions 16 and17 are each fixedly captured within a receiver channel 46. Such dynamictension/compression relationship between the sleeve 14 and the centralconnection portion 8 provides further strength and stability to theoverall assembly.

The illustrated sleeve 14 is substantially cylindrical with an externalsubstantially cylindrical surface 70 and an internal substantiallycylindrical and smooth surface 72 defining a bore with a circular crosssection extending through the sleeve 14. It is foreseen that in someembodiments, the sleeve may be of square, rectangular or othercross-section including curved or polygonal shapes. In the illustratedembodiment, the sleeve 14 further includes a plurality of compressiongrooves 78. Sleeves according to the invention may include one, none orany desired number of grooves 78. Each of the illustrated grooves 78 issubstantially uniform and circular in cross-section, being formed in theexternal surface 70 and extending radially toward the internal surface72. The internal surface 72 is of a slightly greater diameter than asubstantially cylindrical outer diameter formed by the cover 12 thatwraps about the central connection portion 8. The cord cover 12 outersurface is substantially flush with the larger diameter portions 16 and17, resulting in a connecting member with an overall substantiallyuniform outer diameter. The size of the internal surface 72 allows foraxially directed sliding movement of the sleeve 14 with respect to theend portions 16 and 17 and the central portion 8. When the sleeve 14 isreceived about the central connection portion 8, the sleeve 14completely surrounds the central portion 8 as illustrated in FIG. 3. Itis noted that in addition to limiting the bendability of the centralconnection portion 8 and thus providing strength and stability to theassembly 1, the sleeve 14 also keeps scar tissue from growing into theportion 8 through the wound cord cover 12, thus eliminating the need fora sheath-like structure to be placed, adhered or otherwise applied tothe cord cover 12 on the central connection portion 8.

With reference to FIG. 4, the closure structure 32 can be any of avariety of different types of closure structures for use in conjunctionwith the present invention with suitable mating structure on theinterior surface 50 of the upstanding arms 45 of the receiver 41. Theillustrated closure structure 32 is rotatable between the spaced arms45, but could be a slide-in closure structure. The illustrated closurestructure 32 is substantially cylindrical and includes an outerhelically wound guide and advancement structure in the form of a flangeform that operably joins with the guide and advancement structuredisposed on the interior 50 of the arms 45. The flange form utilized inaccordance with the present invention may take a variety of forms,including those described in Applicant's U.S. Pat. No. 6,726,689, whichis incorporated herein by reference. It is also foreseen that accordingto the invention the closure structure guide and advancement structurecould alternatively be a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structure for operably guiding under rotation and advancingthe closure structure 32 downward between the arms 45 and having such anature as to resist splaying of the arms 45 when the closure structure32 is advanced into the U-shaped channel 46. The illustrated closurestructure 32 also includes a top surface with an internal drive in theform of an aperture 80 that may be a hex drive, a star-shaped internaldrive, for example, sold under the trademark TORX or other internaldrives such as slotted, tri-wing, spanner, two or more apertures ofvarious shapes, and the like. A driving tool (not shown) sized andshaped for engagement with the internal drive 80 is used for bothrotatable engagement and, if needed, disengagement of the closure 32from the arms 45. It is also foreseen that the closure structure 32 mayalternatively include a break-off head designed to allow such a head tobreak from a base of the closure at a preselected torque, for example,70 to 140 inch pounds. Such a closure structure would also include abase having an internal drive to be used for closure removal.

In use, at least two bone screws 30 are implanted into vertebrae for usewith the longitudinal connecting member assembly 1. Each vertebra may bepre-drilled to minimize stressing the bone. Furthermore, when acannulated bone screw shank is utilized, each vertebra will have a guidewire or pin (not shown) inserted therein that is shaped for the bonescrew cannula 42 of the bone screw shank 40 and provides a guide for theplacement and angle of the shank 40 with respect to the cooperatingvertebra. A further tap hole may be made and the shank 40 is then driveninto the vertebra by rotation of a driving tool (not shown) that engagesa driving feature on or near a top portion of the shank 40. It isforeseen that the screws 30 and the longitudinal connecting memberassembly 1 can be inserted in a percutaneous or minimally invasivesurgical manner.

With particular reference to FIGS. 2-3, the longitudinal connectingmember assembly 1 that has been factory assembled to include the bumper11, looped ties 10 and the cord cover 12 is assembled with the sleeve 14by inserting either the end portion 16 or end portion 17 into the boredefined by the inner cylindrical surface 72 of the outer sleeve 14. Thesleeve 14 is moved into position over the central portion 8 and betweenthe end portions 16 and 17, thus covering or encompassing the cord cover12.

The connecting member assembly 1 is eventually positioned in an open orpercutaneous manner in cooperation with the at least two bone screws 30with the sleeve 14 disposed between the two bone screws 30 and the endportions 16 and 17 each within the U-shaped channels 46 of the two bonescrews 30. A closure structure 32 is then inserted into and advancedbetween the arms 45 of each of the bone screws 30. The closure structure32 is rotated, using a tool engaged with the inner drive 80 until aselected pressure is reached at which point the end portion 16 or 17 isurged toward, but not completely seated in the channel 46. For example,about 80 to about 120 inch pounds pressure may be required for fixingthe bone screw shank 40 with respect to the receiver 41, Downwardmovement of the closure structure 32 into the channel 46 presses arespective end portion 16 or 17 downward into engagement with a top orother upper portion of the respective bone screw shank 40, pressing arespective retaining structure (not shown) or shank head portion intoengagement with the respective receiver 41, thus setting an angle ofarticulation of the respective shank 40 with respect to the respectivereceiver 41, clamping the shank 40 into a fixed position with respect tothe receiver 41. The receiver 41, the shank 40 and the retainingstructure cooperate in such a manner that the receiver 41 and the shank40 can be secured at any of a plurality of angles, articulations orrotational alignments relative to one another and within a selectedrange of angles both from side to side and from front to rear, to enableflexible or articulated engagement of the receiver 41 with the shank 40until both are locked or fixed relative to each other.

Alternatively, it is foreseen that the capture of the connecting memberassembly 1 by bone screws or other bone anchors and cooperating closurestructures could further involve the use of an upper and/or a lowercompression member or insert disposed within the receiver 41.Furthermore, the assembly 1 may cooperate with an open receiver that isintegral or fixed in position with respect to a bone screw shank or bonehook, or with a receiver having limited angular movement with respect tothe shank, such as a hinged connection, also with or without othercompression members or inserts for fixing the assembly 1, the receiverand/or the bone anchor in a desired position or orientation with respectto the cooperating vertebrae.

Prior to final tightening of the closure structures 32 the members 6 and7 may be pulled away from one another to place the central connectionportion 8 in tension. Also, in certain embodiments, as the closurestructures 32 are rotated and then tightened against the end portions 16and 17 within a pair of spaced bone screws 30, the bone screws 30 may betilted or otherwise pressed toward one another, thereby compressing thesleeve 14. When the insertion and tightening tools are removed, thesleeve 14, pressing against facing surfaces 48 of the cooperating bonescrew receivers 41, placing additional axial tension upon ties 10 andthe cord cover 12 of the central connection portion 8. The assembly 1 isthus substantially dynamically loaded and oriented relative to thecooperating vertebra, providing stress relief (e.g., some shockabsorption) and protected movement with respect to flexing andcompressive forces (and in certain embodiments, if elastic ties and cordcover are utilized, also distractive forces) placed on the assembly 1and the two connected bone screws 30. The ties 10 and the bumper 11 alsoallow the central portion 8 to twist or turn, providing relief fortorsional stresses. The sleeve 14 limits such torsional movement as wellas bending movement of the central connection portion 8, providingspinal support.

If removal of the assembly 1 from any of the bone screw assemblies 30 isnecessary, or if it is desired to release the assembly 1 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 80 on the closure structure 32to rotate and remove the closure structure 32 from the receiver 41.Disassembly is then accomplished in reverse order to the proceduredescribed previously herein for assembly.

Eventually, if the spine requires more rigid support, the connectingmember assembly 1 according to the invention may be removed and replacedwith another longitudinal connecting member, such as a solid rod, havingthe same diameter as the end portions 16 and 17, utilizing the samereceivers 41 and closure structures 32. Furthermore, it is noted thatthe end portion 16 and/or 17 may be elongate, allowing for connection ofa rigid rod portion or portions of the assembly 1 with additional bonescrews or other bone anchors along a patient's spine.

With particular reference to FIGS. 6 and 13, an alternative longitudinalconnecting member assembly embodiment according to the invention,generally 101 includes a flexible cord or cable 105 attached to a rigidmember 107 that is identical or substantially similar to the member 7previously described herein. The cord 105 is both flexible and strongand may be made from a variety of materials including but not limited topolyester fibers that are twisted, plaited, bonded or otherwiseconnected to result in a strong cord or rope. The cord 105 is sized andshaped to be received in a bone screw or other bone anchor 130. The cord105 may be of a polyethylene material as is known in the art for usewith cannulated spacers and cooperating bone anchors. Such a cordtypically extends or stretches somewhat but exhibits little furtherelasticity after being tensioned during implantation.

The member 107 includes a larger diameter portion 117 receivable in thebone anchor 30 previously described herein, a smaller diameter portion121, a tapered portion 125, an end surface 154 and through bores 156spaced in a helical pattern, all of which are identical or substantiallysimilar to the larger diameter portion 17, smaller diameter portion 21,tapered portion 25, end surface 54 and spaced through bores 56 of therigid member 7 previously described herein with respect to the assembly1. Similar to the assembly 1, the assembly 101 has a central connectionportion 108 that includes the smaller diameter portion 121 and furtherincludes a bumper 111, ties 110, a cord cover 112 and an outer sleeve114 identical or substantially similar to the respective bumper 11, ties10, cord cover 12 and sleeve 14 of the assembly 1 previously describedherein. The individual ties 110 are threaded through, integral orintegrally woven into the larger cord or cable 105 and then formdiscrete loops 110 a, 110 b, 110 c, 110 d, 110 e and 110 f that passthrough the bores 156 in the portion 121 of the member 107 in a mannersubstantially similar to the cord loops 10 a, 10 b, 10 c, 10 d, 10 e and10 f extending through the portion 21 of the member 7 of the assembly 1.

The assembly 101 is shown attached to a bone screw 30 previouslydescribed herein at the end portion 117 and to the fixed, closed bonescrew 130 at the flexible cord portion 105. For example, suitable hingedand fixed bone screws for mating with the cord 105 are described inApplicant's U.S. patent application Ser. No. 11/328,481 filed Jan. 9,2006, Publication No. 20060111715, incorporated by reference herein.Although not shown, both the illustrated polyaxial and fixed bone screwseach include a closure structure with a helically wound guide andadvancement structure for mating engagement with the particular bonescrew. Since the bone screw 130 is of a closed, fixed construction themating closure structure (not shown) is a set screw. Furthermore, inorder to securely fix the cord 105 in place, the set screw may includepoints or other protruding structures and/or a compression or holdingmember or insert may desirably be placed between the cord 105 and theset screw or other closure structure.

As with the assembly 1, the assembly 101 readily cooperates with a widevariety of bone anchors and closures, also as previously describedherein at the rigid portion 107 and further cooperates with a variety ofbone anchors adapted for use with cords at the portion 105, and thus isnot limited in use to the particular bone screws disclosed herein.

In use, the longitudinal connecting member assembly 101 is factoryassembled to provide the flexible central transition portion 108 thatincludes the bumper 111 captured between the section 121 and the cord105 by the looped ties 110 as illustrated in FIG. 13 and furtherprotected by the cord cover 112 as shown in FIG. 6. The sleeve 114 isslidable onto both the rigid portion 107 and the corded portion 105, andplacable about the cord covered central or transition portion 108, alsoas shown in FIG. 6. The sleeve 114 (as well as the sleeve 14 previouslydescribed herein) may be cut to the precise desired size by the surgeon.The connecting member assembly 101 is eventually positioned in an openor percutaneous manner in cooperation with the bone screws 30 and 130with the sleeve 114 disposed between the two bone screws 30 and fittingclosely therebetween. The corded portion 105 is tensioned duringinstallation. As with the assembly 1, in certain embodiments accordingto the invention, when the closure structures are inserted into the bonescrews, the sleeve 114 may be compressed by moving the bone screws 30and 130 toward one another during tightening of the closure structureswithin the bone screw receivers. When the insertion and tightening toolsare removed, the sleeve 114, pressing against facing surfaces of theadjacent cooperating bone screw receivers places additional tension onthe ties 110 of the central connection portion 108. The assembly 101 isthus substantially dynamically loaded and oriented relative to thecooperating vertebra. The ties 110 and the bumper 111 also allow thecentral portion 108 to compress and twist or turn, providing relief fortorsional stresses. The sleeve 114 limits such torsional movement aswell as bending movement of the central connection/transition portion108, providing spinal support. Furthermore, if the sleeve 114 iscompressed during installation, the sleeve may extend slightly inresponse to body motion and/or flexion of the transition portion 108,for example.

With reference to FIGS. 7, 8 and 9, dynamic longitudinal connectingmembers according to the invention may include rigid rod portions,flexible cords and flexible cord/rod transition portions in a variety ofcombinations as desired to provide both rigid and/or various levels ofdynamic support of a patient's spine. For example, a third embodimentaccording to the invention shown in FIG. 7 and generally designated 201includes a transition portion or segment 108A substantially identical tothe portion 108 previously described herein and shown in FIG. 6. Howevera rigid rod portion 107A is of a longer length than the rigid portion107 shown in FIG. 6, the rigid portion 107A sized to be received in twobone screws 30.

With reference to FIG. 8, a fourth embodiment according to theinvention, generally 301 includes a central connection or transitionportion 108B identical or substantially similar to the portion 108previously described herein and shown in FIGS. 6 and 13. However, thelongitudinal connecting member 301 includes an extended cord portion105E and an extended rigid portion 107B. The connecting member 301 isthus sized and shaped to attach to at least four bone screws:illustrated herein as two polyaxial screws 30 at the portion 107B, afixed or monoaxial closed bone screw 130 and a fixed open bone screw130′ at the cord 105B. Thus, the member 301 provides an extended lengthof flexible dynamic stabilization at the transition 108B and the cord105B as well as extended rigid support along the rigid length 107B. Twosleeves 114B that are identical or substantially similar to the sleeve14 previously described herein are included in the embodiment 301: onebetween the screw 130 and the screw 130′ and the other between the screw130′ and the polyaxial screw 30. It is further noted that the rigidportion 107B may be straight or curved, pre-bent or curvilinear.

With reference to FIG. 9, another alternative longitudinal connectingmember assembly according to the invention, generally 401 includes aconnection or transition portion 8C identical or substantially similarto the portion 8 previously described herein and shown in FIGS. 1-5 and12 and also a connection or transition portion 108C identical orsubstantially similar to the portion 108 previously described herein andshown in FIG. 6. Thus, the connecting member 401 includes a cord 105Csimilar to the cord 105 of the connecting member 1 and also end portions106C and 107C similar to respective portions 6 and 7 of the connectingmember 1. The connecting member 401 is thus sized and shaped to attachto at least three bone screws: two polyaxial screws 30 at the portions106C and 107C; and a fixed or monoaxial closed bone screw 130 at thecord 105C. Thus there is provided a flexible dynamic stabilization alongthe entire connecting member 401, with both of the transition portions8C and 108C being surrounded and protected by sleeves 114C that areidentical or substantially similar to the sleeve 14 previously describedherein with respect to the connecting member 1.

With reference to FIGS. 14-18 another alternative longitudinalconnecting member assembly according to the invention, generally 501includes a flexible cord or cable 505 attached to a molded plasticmember 507 that may be rigid or have some flexibility, depending uponthe material used to fabricate the member 507. The cord 505 is identicalor substantially similar to the cord 105 previously described hereinwith respect to the connecting member assembly 101 and is shown in FIG.18 received within the closed fixed bone screw 130 previously describedherein. Near an end 508 thereof, the cord 505 includes smaller diameterelongate ties, strands or fibers 510 that are integral, integrallywoven, or otherwise fixed to the cord 505. The cord 505 and the plasticmember 507 may be fixedly attached to one another in a variety of ways.In one embodiment according to the invention, small apertures or holesare drilled in the plastic member 507 at or near the end 520. Suchapertures may be drilled parallel to a longitudinal axis L of theplastic member 507 or at an angle thereto, such as an angle oblique tothe longitudinal axis L. The strands 510 are then inserted or pluggedinto the apertures in the plastic member 507 and adhered to the plasticmember 507 with an adhesive and/or heat. The adhesive may be appliedbefore, during or after plugging of the apertures with the strands 510,with both the adhesive and the strands 510 extending into andpenetrating the member 507 at the drilled apertures.

Also with reference to FIGS. 14-18, alternatively, the strands 510 areembedded into the member 507 during a fabrication process wherein themember 507 is molded adjacent to the cord 505 with the strands 510 beingmolded within the molded plastic of the member 507. Thus, duringfabrication, the plastic flows in and around and bonds to the individualstrands or fibers 510, resulting in a single or discrete longitudinalconnecting member 501 both a corded portion and a solid cylindricalportion. It is believed that certain process parameters, such asperforming the molding process in a vacuum, further aids in the adhesionor bonding of the plastic material to the strands or fibers 510.Longitudinal connecting members according to the invention may includeone or more corded or molded sections along a length thereof. Moldedsections made from different materials may be included along a length ofa connecting member with corded sections disposed therebetween.

With particular reference to FIGS. 15 and 17, the illustrated moldedmember 507 is in the form of a cylindrical rod that includes the end 520that is disposed near or approximately at the end 508 of the cord suchthat all of the strands or fibers 510 are substantially imbedded oradhered within the molded member 507. The molded member 507 may be madefrom a variety of rigid or flexible plastics, including but not limitedto plastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites. It is foreseen that in certain embodiments according to theinvention, the molded member may include elastomeric materials, such asnatural or synthetic elastomers, including, but not limited topolyisoprene (natural rubber), and synthetic polymers, copolymers, andthermoplastic elastomers, and mixtures thereof. Although illustrated asa solid rod with a circular cross-section, the member 507 may have otherforms, including but not limited to oval, square and rectangularcross-sections as well as other curved or polygonal shapes of varioussizes.

The assembly 501 further includes a sleeve or spacer 514 having an outercylindrical surface 570 and a plurality of grooves 578. The sleeve 501is identical or substantially similar to the sleeves 14 and 114previously described herein with respect to the respective assemblies 1and 101. The sleeve 514 receives either the cord 505 or the moldedmember 507 and is eventually operatively positioned over the end 520that is the juncture between the cord 505 of the molded member 507. Inorder to have low or no wear debris, the sleeve 514 inner surfacesand/or outer surfaces of a cooperating portion of the member 507 may becoated with an ultra thin, ultra hard, ultra slick and ultra smoothcoating, such as may be obtained from ion bonding techniques and/orother gas or chemical treatments. It is foreseen that the member 507 maybe sized and made from such materials as to provide for a relativelymore rigid assembly 501 or a relatively more flexible assembly 501 withrespect to flex or bendability along the portion 507. When the portion505 is elongate, sleeves 514 are disposed between bone screws along suchlength. Furthermore, if the member 507 is flexible, sleeves 514 arepreferably disposed between bone screws along the member 507 length.Also, since the distance between the bone screws can vary, the member507 may need to be more or less stiff.

The assembly 501 is shown attached to a bone screw 30 previouslydescribed herein at the member 507 and to the fixed, closed bone screw130 previously described herein at the flexible cord portion 505. Aswith the cord portion 105 previously described herein, suitable hingedand fixed bone screws for mating with the cord 505 are described inApplicant's U.S. patent application Ser. No. 11/328,481 filed Jan. 9,2006, Publication No. 20060111715, incorporated by reference herein.Although not shown, both the illustrated polyaxial and fixed bone screwseach include a closure structure with a helically wound guide andadvancement structure for mating engagement with the particular bonescrew. Since the bone screw 130 is of a closed, fixed construction themating closure structure (not shown) is a set screw. Furthermore, inorder to securely fix the cord 505 in place, the set screw may includepoints or other protruding structures and/or a compression or holdingmember or insert may desirably be placed between the cord 505 and theset screw or other closure structure.

As with the assemblies 1 and 101 previously described herein, theassembly 501 readily cooperates with a wide variety of bone anchors andclosures, also as previously described herein at the solid moldedportion or member 507 and further cooperates with a variety of boneanchors adapted for use with cords at the member 505, and thus is notlimited in use to the particular bone screws disclosed herein.

In use, the longitudinal connecting member assembly 501 is factoryfabricated by a molding and/or machining and bonding process to providea singular longitudinal connecting member having the corded member orportion 505 and a solid molded member or portion 507. The sleeve 514 iscut to the precise desired size by the surgeon for fitting closelybetween the bone screws 30 and 130. The sleeve 514 is then slid ontoeither the molded member 507 or the corded portion 505, and placed aboutthe connecting member 501 at the transition portion indicated by the end520 of the molded member 507 as shown in FIG. 16. The connecting memberassembly 501 is eventually positioned in an open or percutaneous mannerin cooperation with the bone screws 30 and 130 with the sleeve 514disposed between the two bone screws 30 and fitting closelytherebetween. The corded portion 505 disposed between the bone screw 130and the molded member 507 is typically tensioned during installation. Aswith the assembly 1, in certain embodiments according to the invention,when the closure structures are inserted into the bone screws, thesleeve 514 may be compressed by moving the bone screws 30 and 130 towardone another during tightening of the closure structures within the bonescrew receivers. In such embodiments, for example, when the moldedmember 507 has some elastomeric properties, when the insertion andtightening tools are removed, the sleeve 514, pressing against facingsurfaces of the adjacent cooperating bone screw receivers placesadditional tension upon the cord 505 and molded member 507 that make upa transition portion that is disposed between the two bone screws 30 and130. The assembly 501 is thus substantially dynamically loaded andoriented relative to the cooperating vertebra. The sleeve 514 limitstorsional movement as well as bending movement of the cord/rodtransition portion that is disposed between the bone screws 30 and 130,providing spinal support. Furthermore, if the sleeve 514 is compressedduring installation, the sleeve may extend during body motion (withpossible simultaneous distraction of the transition portion if themember 507 includes an elastomeric material).

If removal of the assembly 501 from any of the bone screw assemblies 30or 130 is necessary, or if it is desired to release the assembly 501 ata particular location, disassembly is accomplished by using the drivingtool (not shown) that mates with the internal drives of the cooperatingclosure structures or set screws to rotate and remove such closurestructure or set screw from the bone screws 30 or 130. Disassembly isthen accomplished in reverse order to the procedure described previouslyherein for assembly.

With reference to FIG. 19, an alternative polyaxial bone screw,generally 601 of the invention and an alternative longitudinalconnecting member, generally 605, for use in the invention, areillustrated. The polyaxial bone screw 601 includes a shank 608, areceiver 610 and a retaining and articulating structure 612. The shank608 further includes a threaded shank body 616 and an integral shankupper portion 618. The illustrated receiver 610 includes tool attachmentstructure generally, 620 for cooperating and engaging with an insertiontool. The illustrated receiver 610 is further sized and shaped tocooperate and engage with a closure structure previously describedherein or other suitable bone screw closure structure.

The illustrated longitudinal connecting member 605 cooperates with twoor more bone screws 601 and is a non-fusion dynamic stabilizationlongitudinal connecting member assembly having an outer, cannulatedcoil-like connecting member 630 and one or more threaded inserts 632.Also, a solid cylindrical core or insert (not shown) may replace theinsert 632 and be attached to the core at only one end thereof and beslidingly receivable within the core along a substantial or entirelength of the coil-like member 630. Furthermore, longitudinal connectingmembers made from solid rods or rods having solid or substantiallyhollow portions of non-uniform cross-section may be used with bone screwassemblies and tools according to the invention.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. (canceled)
 2. A medical implant assembly having at least two boneattachment structures cooperating with longitudinal connecting members,the longitudinal connecting members being captured by a closure forlocking each of the bone attachment structures, the medical implantassembly comprising: an elongated solid rod member having a portion atone end thereof attached to a tensionable core member, the rod memberdevoid of a central passageway along an entire length thereof and havinga non-threaded outer surface along an entire length thereof, the rodmember being secured to at least one bone attachment structure by directengagement with the closure; the core member extending between the twobone attachment structures and being in slidable relation with at leastone of the two bone attachment structures when the bone attachmentstructures are locked by the closures; and a compressible outer firstmember positioned entirely between two adjacent bone attachmentstructures, wherein the compressible first member surrounds and engagesa portion of the core member and the first member being held incompression between the two bone attachment structures when the coremember is tensioned, wherein the core member is held in tension by atwo-part end structure including a threaded fastener in direct clampingengagement with the core member, and wherein the fastener is secured tothe core member after the core member is tensioned and the two-part endstructure is compressed against a compressible outer second member. 3.The assembly of claim 2, wherein at least one of the two bone attachmentstructures is a polyaxial bone screw.
 4. The assembly of claim 2,wherein the core member is only tensionable from an end outside of thetwo-part end structure.
 5. A medical implant assembly having at leasttwo bone attachment structures cooperating with longitudinal connectingmembers, the longitudinal connecting members being captured by aclosure, the medical implant assembly comprises: an elongated solid rodmember having a portion at one end thereof attached to a tensionablecore member with an outer non-threaded surface along an entire lengththereof, the rod member being secured to a first bone attachmentstructure by a closure and the core member extending entirely through atleast one additional bone attachment structure and in slidable relationtherewith, such that the core member slides freely with respect to theat least one additional bone attachment structure when the rod member issecured and locked by a closure in the first bone attachment structure;and a compressible outer first member being located entirely between twoadjacent bone attachment structures and engaging a portion of the rodmember and surrounding a portion of the core member, respectively, andbeing held in compression between the two bone attachment structureswhen the core member is held in tensioned by and releasably secured to atwo-part end structure including a threaded fastener in direct clampingengagement with the core member, and wherein the fastener is secured tothe core member after the core member is tensioned and the two-part endstructure is compressed against a compressible outer second member. 6.The assembly of claim 5, wherein the core member is secured to a secondof the bone attachment structures.
 7. The assembly of claim 5, whereinthe rod member is a rigid rod.
 8. The assembly of claim 5, wherein therod member is made from a plastic material, the core member has at leastone flexible tie member extending therefrom, and the tie memberpenetrates the rod member.
 9. The assembly of claim 8, wherein theflexible tie member is bonded to the rod member by an adhesive.
 10. Theassembly of claim 5, wherein the rod member has a plurality ofapertures, the core member has a plurality of flexible tie membersextending therefrom, and each of the flexible tie members extendsthrough a respective aperture of the rod member.
 11. A medical implantassembly having at least three bone attachment structures cooperatingwith longitudinal connecting members, the longitudinal connectingmembers being captured by a closure, the medical implant assemblycomprising: an elongated solid rod member attached to a tensionable coremember, the rod member being secured to at least one bone attachmentstructure, the core member extending between at least two of the boneattachment structures; and a compressible outer sleeve being positionedentirely between two adjacent bone attachment structures; wherein thecompressible sleeve engages a portion of the rod member and surrounds aportion of the core member, the sleeve being held in compression betweenthe two bone attachment structures when the core member is tensioned,wherein the core member extends entirely through at least one boneattachment structure, the core member being in slidable relation withone of the bone attachment structures such that the core member slidesfreely with respect to the one of the bone attachment structures whenthe rod member is secured by the closure to the at least one boneattachment structure, and wherein the core member is held in tension bya two-part end structure including a threaded fastener in directclamping engagement with the core member, and wherein the fastener issecured to the core member after the core member is tensioned and thetwo-part end structure is compressed against a compressible outermember.
 12. The assembly of claim 11, wherein the sleeve engages one ofthe bone attachment structures.
 13. The assembly of claim 11, whereinthe sleeve partially surrounds where the rod member is attached to thetensionable core member.
 14. The assembly of claim 11, wherein the coremember maintains a constant diameter when tensioned.